ssteqr (l) - Linux Manuals
ssteqr: computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method
Command to display ssteqr manual in Linux: $ man l ssteqr
NAME
SSTEQR - computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the implicit QL or QR method
SYNOPSIS
- SUBROUTINE SSTEQR(
-
COMPZ, N, D, E, Z, LDZ, WORK, INFO )
-
CHARACTER
COMPZ
-
INTEGER
INFO, LDZ, N
-
REAL
D( * ), E( * ), WORK( * ), Z( LDZ, * )
PURPOSE
SSTEQR computes all eigenvalues and, optionally, eigenvectors of a
symmetric tridiagonal matrix using the implicit QL or QR method.
The eigenvectors of a full or band symmetric matrix can also be found
if SSYTRD or SSPTRD or SSBTRD has been used to reduce this matrix to
tridiagonal form.
ARGUMENTS
- COMPZ (input) CHARACTER*1
-
= aqNaq: Compute eigenvalues only.
= aqVaq: Compute eigenvalues and eigenvectors of the original
symmetric matrix. On entry, Z must contain the
orthogonal matrix used to reduce the original matrix
to tridiagonal form.
= aqIaq: Compute eigenvalues and eigenvectors of the
tridiagonal matrix. Z is initialized to the identity
matrix.
- N (input) INTEGER
-
The order of the matrix. N >= 0.
- D (input/output) REAL array, dimension (N)
-
On entry, the diagonal elements of the tridiagonal matrix.
On exit, if INFO = 0, the eigenvalues in ascending order.
- E (input/output) REAL array, dimension (N-1)
-
On entry, the (n-1) subdiagonal elements of the tridiagonal
matrix.
On exit, E has been destroyed.
- Z (input/output) REAL array, dimension (LDZ, N)
-
On entry, if COMPZ = aqVaq, then Z contains the orthogonal
matrix used in the reduction to tridiagonal form.
On exit, if INFO = 0, then if COMPZ = aqVaq, Z contains the
orthonormal eigenvectors of the original symmetric matrix,
and if COMPZ = aqIaq, Z contains the orthonormal eigenvectors
of the symmetric tridiagonal matrix.
If COMPZ = aqNaq, then Z is not referenced.
- LDZ (input) INTEGER
-
The leading dimension of the array Z. LDZ >= 1, and if
eigenvectors are desired, then LDZ >= max(1,N).
- WORK (workspace) REAL array, dimension (max(1,2*N-2))
-
If COMPZ = aqNaq, then WORK is not referenced.
- INFO (output) INTEGER
-
= 0: successful exit
< 0: if INFO = -i, the i-th argument had an illegal value
> 0: the algorithm has failed to find all the eigenvalues in
a total of 30*N iterations; if INFO = i, then i
elements of E have not converged to zero; on exit, D
and E contain the elements of a symmetric tridiagonal
matrix which is orthogonally similar to the original
matrix.
Pages related to ssteqr
- ssteqr (3)
- sstebz (l) - computes the eigenvalues of a symmetric tridiagonal matrix T
- sstedc (l) - computes all eigenvalues and, optionally, eigenvectors of a symmetric tridiagonal matrix using the divide and conquer method
- sstegr (l) - computes selected eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix T
- sstein (l) - computes the eigenvectors of a real symmetric tridiagonal matrix T corresponding to specified eigenvalues, using inverse iteration
- sstemr (l) - computes selected eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix T
- ssterf (l) - computes all eigenvalues of a symmetric tridiagonal matrix using the Pal-Walker-Kahan variant of the QL or QR algorithm
- sstev (l) - computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix A
- sstevd (l) - computes all eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix
- sstevr (l) - computes selected eigenvalues and, optionally, eigenvectors of a real symmetric tridiagonal matrix T